INDUCTIVE EFFECTS ATOMIC CHARGES

Atomic Charges, Bond Properties, and Molecular Energies, by Sandor Fliszar Copyright 2009 John Wiley Sons, Inc. 

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Previous studies with a variety of datasets had shown the importance of charge distribution, of inductive effect), of r-electronegativity, resonance effect), and of effective polarizability, aeffi polarizability effect) for details on these methods see Section 7.1). All four of these descriptors on all three carbon atoms were calculated. However, in the final study, a reduced set of descriptors, shown in Table 3-4, was chosen that was obtained both by statistical methods and by chemical intuition. 

Electron Delocalization in the Conjugate Base With a of —1 4 nitnc acid is almost completely ionized m water If we look at the Lewis structure of nitric acid m light of what we have said about inductive effects we can see why The N atom m nitric acid IS not only electronegative m its own right but bears a formal charge of +1 which enhances its ability to attract electrons away from the —OH group... 

The fact that the equilibrium for aminopyridine 1-oxides is displaced further in favor of the amino form than is the equilibrium for aminopyridines is in accord with the mesomerism of these compounds. The stabilization of the amino forms (e.g., 241) by structures of type 240 is more effective than the corresponding stabilization in the pyridine series since the negative charge is associated with the oxygen atom. The stabilization of the imino form (e.g., 242) by structures of type 243 is less than in the pyridine series because of the adverse inductive effect of the oxygen atom. ... 

We can imagine the transition state for alkene protonation to be a structure in which one of the alkene carbon atoms has almost completely rehybridized from sp2 to sp- and in which the remaining alkene carbon bears much of the positive charge (Figure 6.16). This transition state is stabilized by hyperconjuga-lion and inductive effects in the same way as the product carbocation. The more alkyl groups that are present, the greater the extent of stabilization and the faster the transition state forms. 

Phenyltrimethylammonium Ion, N+(CH3)S-CaHe.—In this ion, as in toluene, we ignore the electrons involved in bonds from nitrogen to the attached groups, and consider only the inductive effect. The positive charge on the nitrogen atom increases its electron affinity to a value still greater than that for neutral nitrogen, so that we... 

In the structure on the left, the charge is somewhat stabilized by the inductive effects of the neighboring chlorine atoms. In contrast, the structure on the right is destabilized by the presence of methyl groups. Therefore, the structure on the left is more stable. 

Where the positive charge on the atom adjacent to the nucleus is real rather than formal, i.e. NR3 rather than N02, there is evidence that its effect on o complex stability is exerted through a field effect (cf. p. 22) operating through space, in addition to any polar (inductive) effect operating through the bonds. The deactivating effect of Y on the nucleus declines, i.e. the overall rate of substitution increases, in the approximate order ... 

As with the inductive effect, resonance effects on ground state properties have already been included in the procedure, PEPE, for calculating partial atomic charges. This has been achieved by generating and weighting the various resonance structures of a molecule. The significance and quality of the results has been shown by correlations and calculations of physical data 47>48-52>. 

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